The present invention relates to a tantalum coil for sputtering capable of effectively inhibiting the flaking of sputtered grains accumulated on the surface of a coil that is used in a sputtering device so as to prevent the flakes of such sputtered grains from causing the generation of particles and arcing, and to the method for processing such a coil.
This tantalum coil for sputtering has a curved surface as shown in the diagrams below, and the surface of the coil covers both the inner surface and the outer surface. Accordingly, the expression “surface of the coil” refers to both the inner surface and the outer surface of the coil, and the same shall apply hereinafter.
In recent years, the sputtering method that is capable of easily controlling the film thickness and components is commonly used as one of the methods for depositing materials for use in electronic and electrical components.
The sputtering method employs a principle where: a positive electrode and a negative-electrode target are placed opposite each other; an electric field is generated by applying high voltage between the substrate and the target under an inert gas atmosphere; electrons ionized when the electric field is generated collide with the inert gas to form plasma; the positive ions in this plasma collide with the target (negative electrode) surface to discharge the constituent atoms of the target; and the extruded atoms adhere to the opposing substrate surface to form a film.
As recent sputtering technology, there is a technique of disposing a coil between the sputtering target and the substrate to increase the density of the plasma and to lead as much as possible the flying sputtered grains ballistically toward the substrate. Consequently, the sputtering rate is increased, the uniformity of the film is improved, and the quality of the film that is deposited on the substrate can be comprehensively improved.
There are cases where the material of this coil is sputtered, some are not. It depends on the bias to the coil (refer to Patent Documents 1 and 2).
Accordingly, as the material of the coil, generally used is the same material as the target material, or a material configuring a part of the materials of the sputtered film that is deposited on the substrate. Nevertheless, there is no particular limitation so as long as the coil material does not contaminate the thin film on the substrate. Moreover, as the shape of the coil, there are circular coils and spiral coils (refer to Patent Documents 1, 2, and 3), and there are cases where these coils are disposed in multiple stages.
A problem upon forming a thin film via the foregoing sputtering method is the generation of particles. Generally speaking, the sputtered grains might also be accumulated, other than on the substrate, anywhere such as on the inner wall of the thin-film deposition system or on the internal elements therein. The sputtered grains may be accumulated on the surface other than the eroded portion, or the side surface, of the target. The particles are generated partly because the flakes from the components and the like inside the thin-film deposition system become scattered and adhere onto the substrate surface.
Recently, while the integration of LSI semiconductor devices is increasing (16 Mb, 64 Mb and even 256 Mb), the miniaturization thereof is also improved by decreasing the line width to be 0.25 μm or less. Thus, problems of the disconnection or short-circuiting of the wiring caused by the foregoing particles now occur even more frequently.
Thus, the generation of particles is becoming an even bigger problem while the electronic device circuit continues to be further integrated and miniaturized.
However, when disposing the foregoing coil between a target and a substrate so as to increase the density of the plasma and lead as much as possible the flying sputtered grains ballistically toward the substrate, the amount of sputtered grains that will scatter and adhere, not onto the substrate, but to the inner wall of the thin-film deposition system or to the internal elements therein will decrease; but there is a problem in that the sputtered grains become accumulated on the coil itself.
In order to avoid this kind of problem, Patent Document 3 proposes that the upper end of the inner surface side of the coil is scraped off so as to reduce the thickness of the inner periphery. Here, the provided explanation is that the deposited material to become accumulated at the top of the coil slips off without remaining thereon since the shape of the upper end of the coil becomes sharper toward the top, and the coil is further cleansed since new sputtered grains will collide therewith.
Nevertheless, the portion where the deposited material will accumulate due to sputtering is not limited to the upper end of the coil. There is a possibility that the sputtered grains will also become accumulated on the surface of the coil; that is, on the outer surface and the inner surface of the coil. In the foregoing case, the flakes from the surface of the coil, where the sputtered grains have accumulated, adhere directly to the substrate surface and cause the generation of particles, but no measures are taken for this problem. Based on the demands of higher integration and further miniaturization of the circuit of electronic device, the generation of particles from the foregoing locations will also become a major problem.
In order to resolve the foregoing problem, a proposal has been made to treat the side face of the target and the vicinity of the backing plate via blasting so as to increase the adhesion based on the anchor effect.
Nevertheless, in the foregoing case, there are the following problems; namely, contamination of the product caused by the residual blasting material, flaking of the grains that were accumulated on and adhered to the residual blasting material, and the flaking caused by the selective and non-uniform growth of the adhesive film; and therefore the foregoing blasting is not a final solution. When the coil is particularly made of a hard material like tantalum, it is difficult to even form irregularities by simply performing blasting, and it is not possible to effectively increase the adhesion.
Moreover, Patent Document 4 discloses forming, via knurling, a diamond-shaped or cross-hatch (net-like) pattern on the flange, side wall, shield, covering and the like of a target. Here, the depth is roughly 0.350 mm to 1.143 mm, but since the irregularities on the worked surface are of a simple shape, there is a possibility that a sufficient anchor effect cannot be obtained.
[Patent Document 1] Published Japanese Translation No. 2005-538257 of PCT Application
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2001-214264
[Patent Document 3] Published Japanese Translation No. 2008-534777 of PCT Application
[Patent Document 4] WO2009/099775 (PCT/US2009/031777)